I came up with this magical substance for one of my homebrewed settings, and maybe you can use it in a game.
Angstone Recipe:
Every cubic yard of the stuff needs the ground up bones of a cremated wizard, and the souls / spirits of at least 10 animals / people. If humanoids are used in higher concentrations the substance responds better to the ritual that shapes it. The ritual also summons a base material that is gray and clay-like from another dimension.
The ritual takes one hour for each wizard that was used in the material, but it need not be just one wizard performing the ritual. Others can tag in as long as the ritual is continuously performed. For large Angstone structures it can take weeks, and it might require the "volunteers" from a conquered army / kingdom.
The ritual itself invokes the true names of forgotten / slain gods and goddesses, and if the bones of saints devoted to those deities are used the ritual has a higher likelihood of being successfully completed.
During the ritual the wizard chanting can shape the substance that appears gray into any shape imaginable that often can defy the laws of physics and be painful for mortal eyes to stare long at. Once the ritual is performed successfully the structure takes on a dull black appearance that absorbs most light. Doorways and windows must be thought of during this process, as it cannot be shaped or destroyed afterward.
Large enough structures will bend leylines and other such magical energy lines to them and alter the magical landscape / environment / spirit world.
